#! perl -slw
use strict;
use diagnostics;
use Data::Dump qw[ pp ];

my $diff = 15;

while (<DATA>){
	my $former_time = substr($_, 0, 4);
	my $former_hour = substr($_, 0, 2);
	my $former_mn = substr($_, 2, 2);
	my $new_hour = $former_hour;
	my $new_mn = $former_mn + $diff ;

	if ($new_mn >= 60){
		$new_mn = $new_mn - 60;
		$new_hour = $new_hour + 1;
	}
	# cas où $diff est suffisamment négatif pour faire basculer dans l'heure d'avant
	elsif ($new_mn < 0){
		$new_mn = $new_mn + 60;
		$new_hour = $new_hour - 1;
	}

	my $new_time = "$new_hour"."$new_mn";

	print STDOUT "former_time is $former_time";
	print STDOUT "new time is $new_time";

}


__DATA__
1250
0549
1103
1509
0423
0834